Telephone exchange system



Mam? 1933- E. P. e. WRlGHT TELEPHONE EXCHANGE SYSTEM Filed Nov. 12, 19309 Sheets-Sheet l nvz/avmi? E19 6. WRIGHT 77IMM ATTORNEY March 2-1, 1933-E. P. G. WRIGHT TELEPHONE EXCHANGE SYSTEM Filed'Nov. 12, 1930 9Sheets-Sheet 2 N Gt INVENTOR 5. a. WRIGHT ATT RNEV v March 21, 1933. E,P. G, WRIGHT 1,901,940

TELEPHONE EXCHANGE SYSTEM Filed NOV. 12, 1930 9 Sheets-Sheet 3 INVENTORP.G.WR/GHT ATTOR EV March 21, 1933- E. P. cs. WRIGHT v 1,901,940

TELEPHONE EXCHANGE SYSTEM Filed Nov. 12, 1930 9 Sheets-Sheet 4 IN VE NTOR E.P. G. WRIGHT BY A T TORNEY E. P. G. .WRIGHT TELEPHONE EXCHANGESYSTEM -March 21, 1933.

9 Sheets-Sheet 5 Filed Nov. 12, 1930 lllllll INVEN 70/? 5P. 6. WRIGHT ByA TTDR/ME) March 21, 1933- E. P. G. WRIGHT 1,901,

TELEPHONE EXCHANGE SYSTEM Filed Nov. 12, 19,30 9 Sheets-Sheet 6 l l l I8 8 //vv/v TOR 1 P. G. WRIGHT March 21, 1933. E, "P. G. WRIGHT 1,901,940

TELEPHONE EXCHANGE SYSTEM Filed Nov. 12, 1930 9 Sheets-Sheet '7 //v lENTOR E. P. G. WRIGHT A TDR Y March 21, 1933. E. P. (5. WRIGHT TELEPHONEEXCHANGE SYSTEM Filed Nov. 12, 1930 9 Sheets-Sheet 8 08: l l l l l l l lI l I l 000:8 I u I I I l I l I I l uaoo ve ill l ill .lllll llllliOoneeool II II. \lllI-l Ill llllll ooooooo l I I cuuo IN VEN TOR E. R a.WR/GH r ATTOR Y March 21, 1933. E. P. G. WRIGHT TELEPHONE EXCHANGESYSTEM Filed Nov. 12, 1930 9 Sheets-Sheet 9 lNl/ENTOR '.P. G. WRIGHT BYWPB m 9m ATTORNEY Patented Mar. 21, l3 3 ESIVIOND E.

WEIGHT, OF CROYDON, ENGLAND, ASSIGNOR '10 VIESTEBN ELECTRIC COMPANY,INCGBPOBATED, OF NEW YORK, N. Y., A CORPORATION OF HE /V YORK TELEPHONEEXCHANGE SYSTEM:

Application filed November 12, 1930, Serial No. 495,062, and in GreatBritain December 18, 1929.

This invention relates to telephone exchange systems and moreparticularly to measured service telephone systems in which metering iseffected automatically in accordance with the zone within which thecalled subscribers station is located with respect to the callingsubscribers station.

The object of this invention is to provide simple and efidcient meansfor determining and registering the charge to be made on calls todifferent points all of which are reached in part over a single group oftrunks.

According to this invention means are provided for controlling theoperation of a selector switch so that the brushes are advanced to thesame group of trunks in response to pulses corresponding to any one of aplurality of digits. For instance on calls completed in part over asingle group of trunks to a tandem point the dialing of any of severaldifferent digits is effective to cause selection of this group oftrunks.

Another feature of this invention resides in an arrangement whereby asingle group of trunks is selected in response to impulses correspondingto any one of a plurality of digits, these impulses being at the sametime effective to determine the charge to be made for the establishmentof the call, the charge being varied according to the number of impulsesreceived. Thus in extending calls to and through a tandem oilice thetransmission of any one of several dili'erent digits causes theselection of the same group of trunks to the tandem oi'i'ice but thecharge to be made for each call depends upon its destination beyond thetandem other: and this is indicated by the number of impulses received.

The features of this invention will be better understood from thefollowing description of a telephone system in which the invention isapplied. This system, which is shown diagrammatically in the drawings.is a controller bye-path system equipped with a register-translator foruse on certain classes of calls. It is understood, however, thatmodifications and other applications of the invention will readily occurto one skilled in the art.

Referring to the drawings:

Fig. 1 shows a subscribers station A and line circuit LC, a primaryfinder LFl, a secondary finder LFQ, a group and start unit G, and apre-selector D.

Fig. 2 shows a first selector stage comprising a conversational switchCS1 with which the secondary tinder of Fig. 1 is permanently associated,and a bye-path control unit 01 which is common to a group ofconversational switches including the one shown. The conversationalswitch is separated from the control unit by the broken line.

Figs. 3 and 4 show a second selector stage comprising a conversationalswitch CS2 and a second stage bye-path control unit G2 which is commonto a group of switches including the switch CS2. The broken lineseparates the conversational switch from the common control unit.

Figs. 5 and 6 shows register-translator unit RT which is common to aplurality of second stage control units including the unit C2.

Figs. 7 and 8 show an intermediate selec tion stage comprising theconversational switch CS3 and a bye-path control unit G3 which is commonto a group of switches in cluding the switch CS3. The broken lineseparates the conversational switch from the control unit.

Fig. 9 shows an outgoing trunk repeater 'Tll i for use on calls totandem oflices.

Fig. 10 indicates how Figs. 1 to 9 are to be placed to form the completesystem to which this description relates.

Referring to Fig. 1, A represents a subscribers station which isequipped with a subset of the usual type having a dial for use inautomatically establishing telephone con nections. The line from thisstation terminates at the exchange in a line circuit LC, in the banks ofprimary finders, such as LFl,

' and also in the banks of connector switches,

which are not shown. The line circuit LC includes the usual line andcut-ofi relays and also includes a message register. The subscriberslines are divided into groups and there are as many lines in a group asthere are sets of terminals in the banks of the primary line finders.The primary finder switches comprise 100 point single-motionstep-by-step switches of the no-normal type having two sets of wipersarranged 180 apart, each wiping over an arc of 50 terminals during onecomplete revolution of the switch shaft. The finder LFl includes astepping magnet and the brushes numbered 11, 12 and 13 together withcorresponding banks of terminals.

The lines in each group are mnlt-ipled to the banks of as many primaryfinders as are required to handle the trailic from that group. 1; groupunit is associated with each group of lines; this unit includes a startrelay 6 for starting an idle pie-selected secondary finder in search ofa primary finder whenever a call is originated over any of the lines inthe group.

Zhe secondary finccr switches are similar to the primary finderswitches; the finder LE2 includes a step ing magnet and brushes numberedll t 46 inclusive together with corresponding banks of terminals. Thesecondary finders are linked to conversational switches of a firstselecting stage and are divided into groups each of sufiicient size tohandle the trailic which will be directed through them. Each secondarygroup is arranged to search for a differentprimary finder in each of theprimary groups. Associated with each group of secondary finders is anallotting and controlling switch D which pre-selects an idle secondaryfinder linked witl a first stage selector and having an associatedcontrol circuit which is also idle. Preferably, therefore the number ofpre-selecting switches is equal to the number of groups of secondaryfinders and to the number of primary finders in each group. Thepie-selector D which include the stepping magnet 20 and the brushesnumbered 21 to 28 inclusive together with corresponding terminal banks.is also a single-motion step-by-step switch having no normal position.

hen a subscriber originates a call, the starting relay in the associatedgroup circuit marks all the primary finders serving the group in whichthe call originates, and starts a set of secondary finders, which havebeen preselected by the switches D, in search of an idle primary finder.These secondary finders hunt until two of them have reached markedprimary finders; and those two primary finders then hunt until one ofthem finds the calling line.

The conversational switch CS1 of the first selecting is a 100 pointsingle-motion stcp-by-step switch having a stepping magnetand wipers 51to 54; inclusive. together with corresponding banks of terminals. Thecontrol unit C1 comprises a control s vitch 1L, a bye-path switch and anassociated group of relays. The control switch R1 is a 50 pointstep-by-step single-motion switch, the terminals being strapped so thatin one complete revolution of the switch there are as which the callingline is connec many cycles of operation as the capacity of the switchpermits; this switch includes the stepping magnet and wipers numbered 61to 65 inclusive together vith corresponding banks of terminals. Thebye-path switch R2 is a 100 point single-motion step-by-step switchhaving a stepping magnet and wipers numbered Tl to 76 inclusive togetherwith corresponding terminal hanks. There are two sets each of the wipersdesignated 71, 72, 73 and 74, both sets being eil ective tosimultaneously wipe over corresponding banks of terminals. Certaingroups of po sitions of the switch 1 .1 are used to effect a marking inthe bank of the byepath switch R2, the terminals in these positions ofthe bank 65 being connected as required to the terminals in the controlbank 75 01" switch Qther groups of positions of switch R1 are used foroperatively connecting the control circuit with a particularconversational switch to which a calling line has been er;- tendcd a idthrough which the control circuit is receiving impulses created by theopcration of the chat. at the calling subscribcrs station; the terminalsin these ions of marking banks 74- are multipled to correspondingterminals in the marking ank oi all the conversational switches s thecontrol unit C Outgoing talkin r ductors extend from the ban I theconversational switches of the switching stage. Correspoi ding l testconductors extend from the ban] 4 and 73 of bye-path switch to the svxit hes of the succeeding switching Holding conductors extend irom tl eterminals in the bank 53 of switch CS1 to the conversatioinil switchesof the succeeding switching stage.

The c ntrol switch is advanced under control of the impulses created bythe dialing ot the first digit of the called number to correspondingposition; whereupon the byepath switch P1 is advanced to the groupofterminals thus marked in the banks T l. The switch is then advancedautomatically to select a set of terminals in the marker the testterminal of which is connected through an idle conversational switch oithe succeeding selecting stage to an idle control unit. The incomingimpulse leads are thus immediately extended through brushes 71 and 72 tothe succeeding bye-path control circuit. The R1 switch is then again ivanced until it finds the terminals of the versational switch of thefirst selectin group.

lVhereupon the switch CS1 is advanced un its test brush 54; makescontact. wi .11 t marked terminal corresponding to the set terminalsselected by the bye-path switch Both the control and conversationalconnections are thus extended to the succeeding lecting stage.

The conversational switch CS2 of the second selecting stage, shown inFig. 3, is similar to the switch CS1 of the first selecting se; itincludes the stepping magnet 100 and the brushes 101, 102, 103 and 104together with corresponding banks. The control unit C2, shown in Figs. 3and l, includes the control switches and El /l3 and the byepath switchRM2. The control switch Rlvll is sim lar to the control switch R1 of theing stage; it includes the stepg magnet 110 and the brushes numbered 111to 119 inclusive, together with corresponding banks of terminals. Thebye-path switch B l is similar to the hye-path switch R2 or" the firstselecting stage; it includes the stepping magnet 120 and the brushesnumbered 121 to 126 inclusive together with corresponding banks ofterminals. The control switch REE?) is similar to the bye-path switch3M2: it includes the stepping magnet 140 and the brushes numbered 141 to148 inclusive together with corresponding banks of terminals.

T he register-translator unit RT, shown in igs. 5 and 6, includes afinder switch RF *v means of which the register-translator may beconnected to any one of the group of second stagecontrol units withwhich it is associated. It also includes a code switch a num ricalswitch NS, three sets of e. clays, and a sender switch SM. The

' a single-motion step-byhaving no home position; it has magnet 200 andbrushes numbered 0 inclusive, together with correbanlrs of terminals.The code singleunotion step-by-step normal position; it has a tenningmagnet 220 and brushes numbered nn l i 221 to 225 "ml sive, togetherwith corres nc'inp oanlis of terminals. The numerica switch I? S is asingle-motion step-bystep switch having a normal position; it hasstenpin. magnet 2&0 and brushes numbered 24'! inclusive, together withcorreg )anks of terminals. There are sets or register relays numberedrec-ively from 251 to 25% inclusive, from to 264- inclusive and from 271to 27 1 in- These sets register respectively the n hundreds, and tensdigits of a number in accordance with corrending advances or" thenumerical switch The units digit of a called number is istered by thenumerical switch and does need to be transferred since all of thempulses have then been received. The

r switch SM is single-motion stepswitch having a normal position; iteppinsr nagnet 280 and brushes num- I o 285 inclusive together withcording banlts of terminals.

The second stage control unit receives the second and third digits ofthe office code, and

luring receipt of the third digit a starting signal is extended to anumber of registertranslators causing their various finder switches RFto search for the control unit from which the starting signal wasreceived. The second office code digit is stored by the EM3 switch undercontrol of switch 3M1, and the bye-path switch Rh/l2 selects thecorresponding outgoing trunk group under control of switch RM3. SwitchEl /l2 then automatically selects an idle set of terminals in thisgroup, the test terminal of which leads to a conversational switch ofthe succeeding selecting stage. The third office code digit is stored bythe RM3 switch.

If the call is a local call the register-translator is released as soonas the connection is extended through the bye-path switch RM2 to asucceeding local selecting stage. If the call is an interofiice callreached over direct trunks and an idle trunk is immediately avail able,the register-translator is also released as soon as the connection isextended through the bye-path switch 3M2; but it an idle trunk is notfound before the next digit is dialed, the numerical digits are storedin the registertranslator and retransmitted by its sender switch tocomplete the connection. If the call is one which may be completed overalternative routes,that is, either over a direct trunk selected by thebye-path switch RM2 or over a trunk selected at the intermediateoutgoing selecting stage, the register-translator is released if an idledirect trunk is immediately available. But, if all direct trunks arebusy, the ofice code digits are retransmitted by the control unit C2 tothe register-translator at the same time that the numerical impulses arebeing received; the control unit C2. then operates to advance thebye-path switch RM2 to a group of terminals connected to an intermediateoutgoing selecting stage, and the completion of the connection iscontrolled by the register-translator. If the call is one which iscompleted only through the intermediate selecting stage, the oliice codeand numerical digits are received by the register-translator and thebye-path switch RM2 advances to the group of terminals leading to theintermediate selecting stage. If the call is one which is completedthrough a tandem ofice, the intermediate selecting stage is effective toselect the group of trunks which lead to this tandem oliice although theimpulses transmitted by the register-translator to control the selectionare varied in accordance with the particular called office to be reachedthrough the tandem point.

The intermediate selecting stage, shown in Figs. 7 and 8, comprises aconversational switch CS3, a bye-path control unit C3, and a meteringcontrol switch Z. The control unit C3 comprises a control switch and abyepath switch IE2. The switches CS3, IE1 and IE2 are similar to theswitches CS1, R1 and R2 of the first selecting stage shown in Fig. 2.

The switch CS3 has a stepping magnet 300 and brushes numbered 301, 302,303 and 304 together with corresponding banks of terminals. The switch1R1 has a stepping magnet 320 and brushes numbered 321 to 327 inclusive,together with corresponding banks of terminals. The 1R2 switch has astepping magnet 350 and brushes numbered 351 to 355 inclusive, togetherwith corresponding banks of terminals. The Z switch is a single-motionstep-by-step switch having no normal position; it has a stepping magnet370 and brushes numbered 371 to 374 inclusive, together withcorresponding banks of terminals. The selecting operation of theoutgoing stage is completed in response to impulses received from theregister-translator of the second switching stage in a similar manner tothat in which the selecting operation of the first stage is completed inresponse to the impulses created by the dialing of the first digit ofthe ofiice code. The IE1 switch is also effective to operate the chargecontrol relays 307 and 308 of the switch CS3 according to the positionto which the P51 switch is advanced by the impulses from theregistertranslator. lVhen the superv ory relay 306 of the switch CS3operates 1 consequence of the answer of the called subsc r. a startingsignal is transmitted to the charging switch Z whereby this switch,which is common to a group of conversational swi ches such as CS3, huntsfor and connects to the particular switch whose supervisory relay hasoperated. The charge control circuit is then effective, under control ofrelays 307 and 308 of the conversational switch to operate the callingsubscribers register the required number of times.

The outgoing truck repeater TR shown in Fig. 9 transmits the remainingimpulses sent out from the register-translator RT over the outgoingtrunk to the distant tandem oi'iice T. The tandem oiiice may be equippedwith any of the well known types of automatic telephone apparatus whichresponds to incoming trains of impulses corresponding to the number of acalled station.

The selecting stages for completing local calls or for completing callswhich do not make use of the intermediate selecting stage are notinvolved in the description of this invention and therefore they are notillustrated in the drawings. For the same reason reference to theoperation of the second selecting stage and register-translator on thesetypes of calls will be omitted, as far as possible.

The operation of the system shown in Fi 1 to 9 inclusive will now bedescribed, giving detailed attention to a. call which is routed througha tandem oflice.

When the subscriber at station A removes the receiver to originate acall, an obvious circuit is closed over line 1 for operating the linerelay 2. Relay 2 connects the windings of the cut-oil relay 3 overconductor 5 to mark the sleeve terminal of the line 1 in the banks ofthe associated group of primary line-finder switches. Relay 2 alsocloses a circuit for operating the start relay 6 in group circuit G.

Relay (3 connects the windings of relay 7 over conductor 9 to themarking terminal in the bani-ts of all secondary finders in the associated secondary group. Start relay 6 also connects ground at its outerfront contact, through the outer back contact of relay 7, over conductor8 to operate the start relays such as relay 31, of all the idledistributor switches. One of these operating circuits is traced fromconductor 8 through the normally closed contact of the left-handcontinuity springs of relay 3d, left-hand back contact of relay 36 tothe winding of start relay 31. Relay 31 closes a circuit for operatingrelay 32, from ground at the right-hand bacl: contact of relay 35,through the right-hand front contact of relay 31, winding of relay 32,brush 27 of the distributor switch, ver conductor 48, eft-hand backcontact of relay 55, over conductor (37 to the common control unit- C1,through the outer left-hand back contact of relay conductor 93, backcontacts of relays S6 and 87, conductor 92, inner right-hand backcontact of relay 85, brush 65, and normal terminal of switch R1, normalterminal and brush 75 of switch R2, right-hand back contact of relay 82,and through resistance 79 to battery. As soon as this circuit is closedthe drop in potential across resistance 79 is suiiicient to prevent theselection of any conversational switch in the associated group byanother preselector, similar to D, which is hunting for an idlesecondary finder as hereinafter described. Relay 32 closes a circuitfrom battery through the winding and interrug iter contacts of thestepping magnet l-O of switch LFQ, brush 26, right-hand front contact ofrelay 32, inner right-hand back contact of relay o6, inner left-handback contact of relay 34, to ground at the back contact of relay Thusrelay 32 and the corresponding relay, of each of the distributorswftches which is connected to an idle secondary line-finder, thecontrol circuit of which idle, close the energizing circuit for thestepping magnet of the associated secondary line-finder switches. Relay32 also connects ground through its outer left-hand front contact, theneXt-to-th -outer righthand back contact of relay 36, winding of testrelay 33, and through brush 23 of the distribntor switch to brush 45 ofthe secondary line-finder switch with which the preselector D isconnected.

T he secondary line-finder LF2 is advanced under control of the steppingmagnet -l0 from one terminal to another until the brush 45 reaches themarking terminal to which conductor 9 is multipled, whereupon test relayi for operating relay i tact of relay 3?. inner righthand I e left-handfront a t. isconnecti grcun 3 from tne winding of relay 31.

d o 'ated to the ground at th co L of relay Rewill not operate in relay33, but when rolled by another dis- 'es the marked pritwo test relays 31ate and dis the It apparent, therefore, 7 finders continue to hunt 111have sci' ed primary finders yin recess to the calling line. hesecondary finder stops on the terof a prii. a, tinder which is alreadyengaged, the relay 3 operates in a circuit ich may be trace.fronrbattery through wii'iding, neXt to the inner right-hand backcontact of relay 36, inner left-hand front w contact of relay 32, brushof distributor switch D brush 44- of finder LFEZ terminal the ousyprimary line-under, through the tiple wiring to the correspondlng ternalin the bank of another secondary lineiinder which has alreac yectahlished connec- 1 this primary finder, over a conducspanning toconductor 47, to ground nt cont-act of the relay correspondthe secondaryfinder switch condvance. A primary finder will be 'nto use, however, ifit is idle even if ng on a busy line, since in this case the brush dlwill not be connected to ground at a busy conversational switch.

aforementioned operation of relay 3% c oses a circuit for the steppingmagnet he primary find-er LE1. This circuit e traced from batterythrough the windi and interrupter contacts of magnet l0, te mal andbrush 46 of line-finder L1 2, terminal and brush of banl: 21 ofthdistributor switch D, through the outer right-- front contact of relay34, to ground at the left-hand back contact of relay 35. When t in ay b5/ one of the two hunting primary finders engages the terminals of thecalling lines, a circuit is closed from battery through the windings ofcut-ofi relay 3, in parallel with the winding of the message register l,over conductor 5, through the terminal and brush 13 of line-finder LFl,terminal and brush 43 of line-finder LFQ, terminal and brush 22 ofdistributor swit D, and through the lefthand winding of relay to groundat the neXt-to-the-inner right-hand front Contact of relay Relays 3 and35 are operated by the current in this circuit but the message registera is marginal and does not operate at this time. Gut-off relay 3releases line relay 2 by disconnecting its Winding from the line 1.Relay 2 in turn causes the release of relay 6 unless this relay is heldoperated due to the origination of call over one or more of the otherlines in the group. Relay 35 looks in a circuit from battery through itsrighthand winding, and through thenent-to-thv outer right-hand frontcontact of relay 34, to ground at the left-hand front contact of relay35. Belay 35 opens the circuit for operating the stepping magnet of theprimary finder LFl, opens the circuit through tae winding of relay 32,and closes a circuit from battery through the winding of relay 36,through the middle right-hand front contact of relay 34.- to ground atthe left-hand front contact of relay 35 lhe primary finder IE1 is thusstopped on the terminals of the calling line, relay 32 releases, andrelay 36 operates. Relay 36 opens the circuits through the windings ofrelays 31 and 33 to cause their release; and relay 31 cannot thereafterreoperate if the origination of another call in the same group shouldcause ground to be reconnected to conductor 8. Relay 31 opens thecircuit through the winding of relay 34; and with relays 32 and 34released, relay 36 is held operated through the normally closed contactsof the right-hand continuity springs of relay 3%, inner right-hand frontcontact of relay 36, over conductor 29 to ground at the back contact ofrelay 32. The release of relay 34 causes the release of relay 35. Relay36 closes a circuit for operating relay 56 of the conversational switchCS1 associated with the secondary line-finder used in extending thisconnection this circuit may be traced from battery through the windingof relay 56, over conductor l9, through the terminal and brush of bank28 of distributor switch D, and through the middle left-hand frontcontact of relay 36 to ground at the right-hand front contact of relay35.

The aforementioned release of relay closes a circuit from batterythrough the winding and interrupter contacts of step ingina enet 20 ofdistributor switch B, through the left-hand front contact of relay 36 Fl ir-to-theanner lert-hand hacl: contact or 34, over conductor 29 togro'und at the left-hand back contact of relay 32. The distributorswitch D is thereby advanced to preselect an idle secondary finder whosecontrol circuit is also idle in readiness for the next call. lVhen theterminals of such a secondary finder are reached, relay 32 operates in acircuit from ground at the right-hand back contact of relay 35, outerleft-hand front contact of relay 36, winding of relay 32, brush 27 andterminal of switch D, over conductor 48, through the back contact ofrelay 55 of the associated conversational circuit, over conductor 67 tothe associated control circuit, and thence to idle battery in av similarmanner to that hereinbefore described for the operation of relay 32 uponthe origination of a call over line 1. Relay 32 opens the circuit forstepping magnet 20 and opens the locking circuit for relay 36. Therelease of relay 36 in turn ca'uses the release of relay 32. Should thedistributor switch D engage a secondary finder which, although idle, hasbeen preselected by another distributor switch, relay 37 is operated, leiore relay 36 releases, in a circuit from battery through he winding ofrelay 37, next-to-the-inner right-hand front contact of relay 36, brushand selected terminal of bank 24, through the brush 2% of thepreselector which has already selected this secondary finder, to groundat the outer righthand front contact of the relay which corresponds torelay 36. Relay 37 connects ground from the outer right-hand frontcontact of relay 36 through the right-hand front contact of relay 37 toconductor 29 to hold relay 36 operated and thus continue stepping thepreselector brushes past this terminal. Relays 32 and 37 release whenthe br'ushes are advanced so that the preselector continues to huntuntil another idle secondary finder is reached.

The aforementioned operation of relay 56 extends the connection from thecalling line 1, through brushes l1 and 12 of primary finder LFl andbrushes $1 and 42 of secondary finder LF2. right-hand front contacts ofrelay 56, conducc (3S and outer left-hand back contacts of relay 88, tothe windings of impulse relay 81 of the control unit Cl. Relay 81operates thereby closing an obvious circuit for operating relay 32.Relay 56 also connects ground throi its left-hand from contacts, throughbrush of line-finder LF2 and brush 13 of line-finder LFl to hold thecut-off relay 3 of the calling subscribers line operated, and thusprevent release of the connection. Relay 82 connects ground at its outerleft-hand front contact to conductor 93, thereby locking relay 56through its winding and right inner front contact. Relay also opens thetest circuit over conductor 6. and through resistance 7 9, so as toprevent the seizure of any other conversational switch associated wi hthe control unit C1. Relay 8% now operates in a circuit which may betraced from battery through its winding, right outer back contact ofrelay 88, next-tothe-inne right front contactof relay 82, brush andnormal terminal of bank of switch B2, normal terminal and brush (35 ofswitch R1, inner right back contact of relay 85, over conductor 92,through the back contact of relays 8'? and 86, over conductor 93 toground at the left outer front contact of relay 82. The secondarywinding of transformer 30 connected through the mid :lle left backcontact of relay 85, in parallel with the leftnand winding of relay 81so that dial tone 1S transmitted to the calling subscribers station asan indication that dialing of the called number may be in.

i l en the calling subscriber dials the first i reeases and reoperateseach time the line circult is opened and closed at the dial contacts.Relay 82 is a slow-to-release relay and res operated during the receiptof the ntire train of impulses. The release of relay 1 closes a circuitfrom battery through the OOKD winding of magnet 60 of switch R1, throughtie left outer back contact of relay 85, left inner front contact ofrelay 82, winding of relay 83, to ground at the right-hand bacl: contactof relay 81. Magnet (30 and relay 83 both operate in this circuit. Relay83 is also a slow-to-release relay and holds operated during receipt ofthe entire train of impulses. The reoperation of relay 81 causes therelease of magnet 60, thereby advancing the switch into position Belayreleases when the brushes of switch R1 advance from position 1, thenormal position. Each release and reoperation of relay 81 thus causesthe peration and release of magnet 60 thereby advancing the brushes ofswitch R1 to a position which corresponds to the digit dialed.

The aforementioned release of relay 8i, when the brushes of switch R1are advanced from position 1 to position 2, closes a circuit frombattery through the winding of stepping magnet 70 of switch R2, middleright hand back contact of relay 88, interrupter cont-acts of magnet 70,right-hand back contact of relay 8st, brush and normal terminal of bank76 of switch R2, front contact of relay 83, and through the backcontacts of relays 87 and 86 to ground on conductor 93. When magnet 70operates, the circuit through its winding is opened and magnet 70releases, thereby advancing the brushes of switch R2 to position 2.lVith switch R2 in any position other than its normal position theconnection from the winding of magnet 70 to brush 76 is extended throughthe off-normal terminals of bank 76 to ground at the right outer backcontact of relay 85. Switch R2 is thereafter advanced under control ofits own interrupter contacts until relay 84 reoperates as hereinafterdescribed. The terminals in bank 65 of switch R1 are connected lit) tothe terminals in bank of switch R2 in such a manner that the circuit forreoperating relay 84 is completed whenever the R2 switch reaches thebeginning of the group which corresponds to that on which the R1 switchis standing after all of the impulses created by the dialing of thefirst digit have been received( The circuit for reoperating relay 84:may be traced from battery through its winding, right outer back contactof relay 88, right outer front contact of relay 82, brush 75 andterminal of switch R2, the corresponding terminal and brush of bank 65of switch R1, inner right back contact of relay 85, over conductor 92,and through the back contacts of relays 87 and 86 to ground on conductor93. When relay 8% reoperates in this circuit, it opens the circuit foroperating magnet 70 to stop the brushes of switch E2 on the first set ofterminals in a group which corresponds to the first digit dialed by thecalling subscriber.

The reoperation of relay 84 closes a circuit for operating relay thiscircuit may be traced from battery through the left-hand winding ofrelay 85, left outer back contact of relay 91, left-hand back contact ofrelay 83, right-hand front contact of relay 84, brush and terminal ofbank 76 to ground at the right outer back contact of relay 85. Relay 85closes a locking circuit through its right-hand winding and innerright-hand front contact to ground over conductor 93 before the circuitthrough its left-hand winding is opened at its outer right-hand backcontact. The operation of relay 85 causes the release of relay s4 andconnects the windings of test relays 86 and 87 to test brushes 78. Ifthe first set of terminals of the selected group are idle, one or bothof test relays 86 and 87 operate, depending upon which of the brushes 73is in contact with an idle set of terminals. The circuit for operatingrelay 86 may be traced from ground on conductor 98, through the rightouter back contact of relay 91, winding of relay 86, left inner backcontact of relay 88, neXtto-the-outer right-hand front contact of relay85, lower brush 7 3 and first terminal in the selected group, overconductor 98, left outer back contact of relay of the selectedconversational switch CS2 in the next switching stage, over conductor106 to the associated control unit C2, through the left-hand backcontact of relay 189, normal terminal and brush 111 of switch RMl, rightouter back contact of relay 130, upper brush 12 1 and the normalterminal of the corresponding bank of switch RM2, and through resistance127 to battery. The circuit for operating relay 87 may be traced fromground on conductor 98 through the winding of relay 87, middleright-hand back contact of relay 91, neXtto-the-inner left-hand backcontact of relay 88, middle right-hand front contact of relay 85,through the upper one of test brushes 7 8 and the first terminal of theselected group, thence over a conductor similar to conductor 98, tobattery in a control unit in the same manner as already traced for theoperation of test relay 86. The operation of either or both of relays 86and 87 prevents the further advance of the brushes of switch R2 sincethe circuit for operating magnet 70 passes through the back contacts ofboth of these relays. If the first sets of terminals in theselectedgroup are busy, stepping-magnet (O is reoperated in a circuit which maybe traced from battery through its winding, middle right-hand backcontact of relay 88, interrupter contacts of magnet 70, right-hand backcontact of relay 83, brush 76 and terminal with which it is in contact,right outer front contact of relay 85, conductor 92, and through the bacr contacts of relays 87 and 86 to ground on conductor 98. The brushes ofswitch are thus advanced until an idle set of terminals is reached andeither or both of relays 86 and 87 operate or until the brushes reachthe last of terminals in, the selected group. If relay 86 operates itcloses an obvious circuit for operating relay 88; and relay 88 looksthrough its inner righthand front contact to ground on conductor 93. Ifrelay 87 operates, and relay 86 is not operated, it closes an obviouscircuit for operating relay 89;-and relay 89 closes an obvious circuitfor operating relay 88. Relay 88 looks to ground on conductor 98; andrelay 89 is looked through its inner left-hand front contact and theinner right-hand front contact of relay 88 to the same ground. Relay 89controls the connections to brushes 71, 72 and 76% trender either theupper or lower of these brushes effective, to the exclusion of theothers, dependin upon whether the selected set of terminals 15 locatedin the upper or the lower of the corresponding banks. In the followingdescription we will assume that the selected terminals are located inthe lower one of banks 71, 72 and 73 so that relay 89 is not operated.Test relays 86 and 87 are released by relay 88 after it has lockedoperated.

If all of the terminals of the selected group are busy, a circuit isclosed from battery through the winding of relay 8%, right outer backcontact of relay 88, outer right-hand front contact of relay 82, brushand last terminal in the selected group of bank 75, nextto-the innerright-hand front contact of relay 85, conductor 92, back contacts ofrelays 87 and 86, to gro nd on conductor 93. Relay 8% opera es in thiscircuit, to prevent the further operation of stepping magnet 70. Relay8% closes circuit from batte v through the winding of of relay 85, 11"1-hand front contact of relay 8%, brush and of-norinal terminals of bank76, through the outer right-hand front contact of relay 85, overconductor 92, and thence to ground as hereinbefore traced. Relay 91 is aslow-to-operate relay so that it will not operate in this circuit duringthe intervals that both relays 84 and 85 were operated at the time ofthe initial operation of relay 85; but on the last set of terminals in agroup the circuit for relay 91 is maintained so that relay 91 eventuallyoperates and connects busy tone through the secondary winding oftransformer 90, right inner front contact of relay 91, middle left-handfront contact of relay 85 in parallel with the left-hand winding ofrelay 81, so that the all-trunksbusy signal is transmitted to thecalling subscriber.

The aforementioned operation of relay 85, at the time of the completionof group selection by switch R2, was also effective to close a circuitfor operating stepping magnet of switch R1 so as to advance the brushesof switch R1 into engagement with the set of terminals through whichitis connected to the conversational switch CS1. The circuit foroperating magnet 60 may be traced from battery through its winding,through the outer left-hand front contact of relay 85, interruptercontacts of magnet 60 to ground at the back contact of relay 66. Thestepping magnet 60 is therefore alternately operated and released andthe brushes of switch R1 are advanced one step by each release of themagnet 60. When brush 61 makes contact with the terminal associated withswitch CS1, relay 66 operates in a circuit which is traced from batterythrough its winding, brush and terminal of bank 61, right inner frontcontact of relay 56, over conductor 93 to ground at the left outer frontcontact of relay 82.

VVit-h relays 66 and 88 both operated (due to the fact that the R2switch has found an idle set of terminals in the required group, andthat the control unit C1 is connected through the brushes of switch R1to the conversational switch CS1), a circuit is completed for operatingthe stepping magnet 50 of the conversational switch CS1; this circuit istraced from battery through the wind ing and interrupter contacts ofmagnet 50, terminal and brush of bank 64 of switch R1, left-hand backcontact of relay 84, and through the outer right-hand front contact ofrelay 88 to ground at the lefthand front contact of relay 66. Relay 66also connects the ground on conductor 93 through the back contacts ofrelays 86 and 87, conductor 92, right-hand front contact of relay 66,and through the brush and terminal of bank to the test brush 54 ofswitch CS1. Magnet 50 advances the brushes of switch CS1 until the testbrush 54 comes into contact with the terminal in its bank which isconnected to the terminal of the selected set in the bank 74 of switchR2, thereby extending the ground on test brush 54 through brush 74, themiddle right-hand back contact of relay 89, and through theneXt-to-the-outer right-hand front contact of relay 88, to the windingof relay 84. Relay 84 operates, thereby opening the circuit foroperating the stepping magnet 50 so as to stop the brushes of switch CS1on the terminals of the outgoing eonversational switch which waspreviously s lected by the byepath switch R2. Belay 84 closes a circuitfor operating relay 91; this circuit is traced from battery through thewinding of relay 91, left inner front contact of relay 85, right-handfront contact of relay 84, brush and terminal of bank 7 6 of switch R2,right outer front contact of relay 85, conductor 92, back contacts ofrelays 87 and 86, to the ground on conductor 93. Relay 91 closes acircuit from battery through the winding of relay 55 of conversationalcircuit CS1, terminal and brush of bank 63 of switch R1, left outerfront contact of relay 91, left-hand front contact of relay 84, rightouter front contact of relay 88, to ground at the left-hand frontcontact of relay 66. Relay 55 locks through its right outer and leftinner front contacts and through the outer left-hand front contact ofrelay 56 to ground at the inner left-hand front contact of relay 56.Relay 55 extends the talking connection, from brushes 41 and 42 ofline-finder LF2, through its inner right-hand front contacts, throughbrushes 51 and 52 of switch CS1, over trunk 99 to the conversationalswitch CS2. It also extends the ground at the inner left-hand frontcontact of relay 56, through the left outer front contact of relay 56and the left inner front contact of relay 55, through brush 53 of switchCS1 over the sleeve conductor of trunk 99 to mark the associatedconversational switch CS2 in the bank 118 of switch RMI in the controlunit C2.

The aforementioned operation of relay 88, after switch R2 finds an idleof terminals in the selected group, is effective to disconnect thewindings of line relay 81 from the calling line and to extend theconnections from the calling line through its outer left-hand frontcontacts, the inner and outer right-hand back contacts of relay 89,through the lower brushes and selected terminals in banks 71 and 72,over conductors 96 and 9?, to the control unit C2 of the succeedinselecting stage. Relay 88 also extends conductor 93. through theleft-hand back conta ct of relay 89, the inner left-hand front contactof relay the neXt-to-thc-outer right-hand front contact of relay 85,through the lower brush and terminal of bank 7 over conductor 98 to thecontrol unit C2. Relays 81 and 8:2 release in consequence of theoperation of rela but relays 56, 85 and 88 (also 89, if operated) areheld operated by ground connected to conductor 98 as is hereinafterexplained.

lift

. mal.

Impulses created by the dialing of succeeding digits of the callednumber are, therefore, transmitted through control unit C1 to controlunit C2, until the control unit C2 5 disconnects this ground fromconductor 98, at which time relays 56, 85 and 88 are released. Relay isheld operated through its right outer front contact and brush 53 ofswitch CS1, over the sleeve conductor of 0 trunk 99 to ground in controlunit C2 as is hereinafter described. The release of relay 56 cause thesuccessive release of relays and 84 and the release of relay 66 closes acircuit for advancing the R1 switch to nor- The circuit for operatingstepping magnet is traced from battery through its winding, left outerback contact of relay 85, left inner back contact of relay 82, rightinner back contact of relay off-normal 0 terminals and brush 62 ofswitch R1, interrupter contacts of magnet 60. to ground at the backcontact of relay 66. The release of relay 84 closes a circuit foradvancing the R2 switch to normal; this circuit is traced 5 from batterythrough the winding of stepping magnet 70, middle right-hand backcontact of relay 88, interrupter contacts of mag net 7 O, right-handback contact of relay 8%, brush and elf-normal terminals of bank 76, toground at the right outer back contact of relay 85. With both ofswitches R1 and R2 in their normal positions, the control unit C1 ismade available for use with another of the associated conversationalswitches since the 5 test conductor 67 is new again connected throughresistance 79 to battery.

JVhen the connection from the calling line is extended through brushes71 and 72 of switch R2 of control unit C1, line relay 131 Q of controlunit C2 is operated in a circuit which may be traced from batterythrough the right-hand winding of this relay, right outer back contactof relay 165, next-to-the outer right-hand back contact of relay 166, 5over conductor 96, through the lower bank and brush 71 of switch R2 incontrol unit C1, outer right-hand back contact of relay 89, outerlefthand front contact of relay 88, conductor 68, outer right-hand frontcontact of 0 relay 56, brush d1 of line-finder L1 2, brush 11 ofline-finder LF1, line 1 and the calling subscribers sub-set, brush 12 ofline-finder L1 1, brush 42 of line-finder LF2, middle right-hand frontcontact of relay 56, conduc- 5 tor 69, neXt-to-the-outer left-hand frontcon tact of relay 88, inner right-hand back contact of relay 89, throughthe lower brush and terminal of bank 72 of switch R2, conductor 97,next-tothe-inner right-hand back 0 contacts of relays 166 and 165,through the left-hand winding of relay 131 to ground. Relay 131 closesan obvious circuit for operating the slow-to-release relay 131. Relay132 closes a circuit for operating relay 130, from battery through thewinding of relay 130, right outer back contact of relay 166, overconductor 129, to ground at the front contact of relay 132. Relay 130opens the aforementioned test circuit through the brush and normalterminal of bank 124 and connects ground through its left outer frontcontact, the left outer back contact of relay 139, conductor 106, theleft outer back contact of relay 105, over test conductor 98, terminaland lower brush 7 3 of switch R2 of control unit C1, neXt-to-the-outerright-hand front contact of relay 85, left inner front contact of relay88, left outer back contact of relay 89, to holding conductor 93 ofcontrol unit 01; this ground is effective to prevent the release ofrelays 55, 56, 66, 8t, 85 and 88 as hereinbefore mentioned.

When the calling subscriber dials the seeone digit, this being one ofthe digits of the office code, line relay 131 of control unit C2 isalternately released and reoperated as many times as its operatingcircuit is opened by the contacts of the dial. The release of relay 131closes a circuit for operating the stepping magnet 110 of switch RMl andrelay 133 this circuit is traced from battery through the winding ofstepping magnet 110, right inner back contact of relay 136, right innerfrontcontact of relay 130, winding of relay 133, to ground at the backcontact of relay 131. VJhen relay 131 reoperates, the stepping magnet110 releases but relay 133 is a slow-to-release relay and it remainsoperated until all of the pulses corresponding to the second digit havebeen received. Since relay 132 is also a slow-to-release relay itremains operated during receipt of this train of impulses. The brushesof switch RMl are thereby advanced by the alternate operation andrelease of mag net 110 to a position which corresponds to the seconddigit dialed by the calling subscriber.

hen the switch Rlvll reaches position 2, a circuit is closed foroperating the stepping maknet 140 of switch 3M3; this circuit is tracedfrom battery through the winding and interrupter contacts of magnet 110, brush and normal terminal of bank 145, over conductor 128, throughthe second terminal and brush of bank 111 of switch Rllll, middle rightback contact of relay 136, over conductor 129 to ground at the frontcontact of relay 132. Stepping magnet 120 of switch RM2 is also operatedwhen the brushes of switch RMl enter position 2, since the winding ofmagnet 120 is then connected, through its interrupt-er contacts andthrough the brush and normal terminal of bank 126, over conductor 128 tothe second terminal of bank 111 of switch El /l1. The release of magnets140 and 120 when their circuits are opened by their own interruptersprings causes the advance of switches RM2 and RM3 from their normalposition to position 2. The terminals of bank 112 of switch RMl areconnected in pairs to ice the terminals of bank 148 of switch RM3; toillustrate, terminals 2 and 3 of bank 112 are connected to terminal 2 ofbank 148, and terminals 4 and 5 of bank 112 are connected to terminal 12of bank 148. lVhen, therefore, the brushes of switch RM3 are advancedinto position 2, a circuit is completed from battery through the windingof, relay 134, brush and terminal 2 of bank 148, through terminal 2 or 3and brush of bank 112 of switch Rldl, right-hand back contact of relay139, to ground at the left inner back contact of relay 158. Inoperating, relay 134 prevents the closing of another operating circuitfor the stepping magnet 140 so that switch RM3 remains in position 2until switch RMl has advanced beyond position 3. If, and when thebrushes of switch RMl are advanced beyond position 3 in response toimpulses received by line relay 131, relay 134 releases; and the circuitfor operating magnet 140 to cause the further advance of switch 3M3 istraced from battery through the winding and interrupter contacts ofmagnet 140, brush and oil-normal terminals of bank 145, back contact ofrelay 134, to ground at the left-hand back contact of relay 136. Whenthe brushes of switch RM3 reach position 12, the circuit for operating134 is again closed; and the operation of relay 134 prevents the furtheradvance of switch RM3 until the brushes of switch RMl have been advancedbeyond position 5. The stopping positions 2, 12, 22, etc. of switch RM3represent the first terminals of different routing groups in the banks141 and 142. The first and succeeding terminals of each group ofterminals in banks 141 and 142 are connected to the first terminal of acorresponding group of terminals in bank 125 of switch RM2. The firstterminal of each group in bank 125 is thus continuously marked while thebrushes 141 and 142 are engaging the corresponding terminals in theirrespective banks. This arrangement prevents the advance of switch RM2beyond the first terminal of the group marked by switch RM3. The windingof relay 149 is connected to terminals 3, 5, 7, 9, and 11 of bank 111 ofswitch RMl so that this relay is operated, through brush 111 in each ofthese positions; to the ground on conductor 129, but the operation ofrelay 149 during the receipt of the impulses created by the dialing ofthe second digit is without effect since at this time brush 142 iscontinuously connected through the right outer back contact of relay 136and the left-hand back contact of relay 168, to ground at the rightouter back contact of relay 158.

Having advanced from normal to position 2 the further advance of switchRM2 is controlled by relay 135, this relay being connected to operatewhen brush 125 of switch RM2 engages the terminal marked by brushes 141and 142 of switch RM3. The circuit for operating relay 135 may be tracedfrom battery through its winding,'right outer back contact of relay 162,brush and marked terminal of bank 125 of switch RM2, terminal and brushof bank 141 or 142, through the left inner front contact of relay 149 orthe right outer back contact of relay 136, and through the left-handback contact of relay 168, to ground at the right outer back contact ofrelay 158. The circuit for operating magnet 120, after the brushes ofswitch RM2 have been advanced to position 2, may be traced from batterythrough its winding and interrupter contacts, brush and off-normalterminals of bank 126, left inner back contact of relay 162, backcontacts of relay 135, 157 and 156, to ground at the middle lefthandback contact of relay 162. If and when the brushes of switch RM3 areadvanced beyond the first group, as controlled by the setting of switchRMl, the stepping magnet of switch RM2 will be again energized due tothe release of relay 135; and the brushes of switch 3M2 will be advanceduntil they engage the next terminal which is marked by brush 141 or 142of switch RM3, at which time relay 135 reoperates in the circuitiereinbefore traced. Vfith both of relays 134 and 135 operated and withrelay 133 released, a circuit is completed for operating relay 136. Thiscircuit may be traced from battery through the left-hand winding ofrelay 136, front contact of relay 134, right-hand back contact of relay133, front contact of relay 135, back contacts of relays 157 and 156, toground at the middle left-hand back contact of relay 162. Relay 136closes a locking circuit through its right-hand winding andneXt-to-the-inner right-hand front contact, to ground at the left innerfront contact of relay 130. Relay 136 opens the circuit for operatingmagnet 140 of switch RM3, disconnects the back contact of relay 131 fromthe magnet 110 of switch RMl and connects the back contact of relay 131to magnet 140 of switch RM3 in readiness for storing the next train ofdial impulses.

If switch R-Ml stopped in one of positions 3, 5, 7 9 or 11 so that relay149 is operated and if the circuit for operating relay 135 passesthrough brush and bank 142 instead of through brush and bank 141, relay135 releases when relay 136 operates and relay 149 is locked through itsright-hand front contact and the right outer front contact of relay 136,to ground on conductor 129. The release of relay 135 again closes thecircuit for operating magnet 120 of switch RM2 so as to advance thebrushes of this switch until they reach the terminal which is marked bybrush 141 instead of brush 142 of switch RM3. Relay 135 then reoperatesto stop further advance of switch RM2. Thus relay 149 controls themarking circuit through brushes 141 and 142 depending upon the firstdigit dialed. In the following description we will assume relay 14.9 tobe normal so that brushes 142, 14a and 1 1-? are operatively effectiveto the exclusion of brushes 1e11, 1 13 and 146.

To sum up the operation due to the dialing of the second oflice codedigit relay switch 3M1 is advanced to a position which corresponds tothe number of impulses received. Switch EMS is thereby advanced to acorresponding routing group in order to marl a group terminal in thebank of switch E1112. Switch 3M2 is thereupon advanced under control ofswitch 3M3 to the first terminal of a group which leads toward theexchange or exchanges indicated by the second oilice code digit. Relay13%- operates when switch El /l3 has been advanced to the terminalmarked by switch EH1 and relay 135 operates when switch EH2 has beenadvanced to the terminal marked by switch R113.

The aforementioned operation of relay 136 also closes a circuit foroperating stepping magnet 110 of switch Eli l1 to advance the brushes ofthis switch to connect with conversational switch CS2; this circuit maybe traced from battery through the winding of magnet 110, right innerfront contact of relay 136, back contact of test relay 137, andinterrupter contacts of magnet 110 to ground. The brushes of switch RMlare thereby advanced by the alternate operation and release of magnet110 until the terminals associated with the conversational switch CS2are reached, at which time a circuit is completed for ogerating testrelay 137. Relay 13d releases when switch RMl advances. The circuit foroperating test relay- 137 may be traced from battery through the windingof relap 13?, resistance 138, brush and terminal of bank 118, backcontact of the continuity springs of relay 105, over the holdingconductor of trunk 99, through the terminal and brush 53 of switch CS1,the left inner front contact of relay 56, and through both left frontcontacts of relay 55 to ground. Relay 13? opens the operating circuitfor magnet thereby preventing the further advance of switch Rldl. Relay137 also closes an obvious circuit for operating relay 139. Relay 139disconnects the ground at the left out-er front contact of relay fromtest conductor 98 and connects this ground hrough the left outer frontcontact of relay 139, through the brush and terminal of bank 118, backcontact of the continuity springs of relay 105 over the sleeve conductorof trunk 99, through brush 53 of switch CS1 and the right outer frontcontact of relay 55 to the winding of relay 55 to hold this relayoperated after relay 56 is released. Relays 56,66, 84, 85 and 88 of thesecond selecting stage release when the ground over conductor 98 is thusdisconnected by the operation of relay 139 from conductor 93 of controlunit C1, thereby causing the return of this control unit to normal ashereinbefore described. The impulsi'ng circuit from line 1 is now tracedthrough the inner right-hand front contacts of relay 55, brushes 51 and52 of conversational switch CS1, over the talking conductors of trunk99, through the terminals and brushes of banks 116 and 117 of switchRMl, the left inner front contacts of relay 139, the back contacts ofthe right-hand inner continuity springs of relay 166, and through theouter r ht-hand back contacts of relay 165 to the windings of line relay131.

When the calling subscriber dials the next digit (the third digit of theofiice code), relay 131 is alternately released and reopera'ed inresponse to the impulses thus cretet. The first release of relay 131closes a circuit for operatingmagnet of switch T1113 and slow-to-releaserelay 133; this circuit may be traced from battery through the windingof magnet 140, middle left back contact of relay 159, outer left backcontact of relay 162, neXt-to-the-inner left-hand back con 'act of relay166, inner left front contact of relay 136, right-hand front contact ofrelay 130, winding of relay 133, to ground at the back contact ofrelay131. The operation of relay 133 closes a circuit for operating relaythis circuit may be traced from battery through the winding of relay150, left outer front contact of relay 136, next-to-theouter left-handback contact of relay 166, left outer front contact of relay 133 toground on conductor 129. Relay 150 locks in a circuit from batterythrough its winding, the left outer front contact of relay 136, rightouter front contact of relay 150, left outer back contact of relay 158,and through the normally closed contacts of the left-hand con tinuitysprings of relay 166, to the ground on conductor 129. Relay 150 sends astarting signal to all of the register-translators associated with thecontrol unit C2 by connecting the ground at the outer back contact ofrelay 170, through the left outer front contact of relay 150, toconductor 180. Relay 150 also connects battery through the windings ofrelay 170, the middle left front contact of relay 150, left outer backcontact of relay 159, to the test terminal associated with control unitC2 in the bank 209 of the register-translator RT and the correspondingterminals in the banks of the other associated register-translators.

The alternate operation and release of magnet 140, in response to theimpulses received by relay 131 from the dialing of the third digit,causes the advance of the brushes of switch RM3 to a correspondingterminal in the previously selected routing group. 17 hen relay 133releases after all of the im pulses corresponding to the third digithave been received, a circuit is closed for operating relay 151; thiscircuit is traced from battery through the winding of relay 151, outerlefthand back contact of relay 133, neXt-to-the- SOY

